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s Au = 0.65 ps was determined from transient bleach experiments [9], ands Pt = 0.17 ps was calculated from electrical conductivity data [47]. The calculationsand experiments are in excellent agreement. Essentially perfectagreement can be obtained by allowing the time constant for Pt to vary. Thisyields a characteristic electron–photon coupling time for Pt of 0.22 ps (inclose agreement with the value calculated from the conductivity of Pt). NoteFigure 8 (a) Transient absorption data for pure Au particles (47 nm in diameter)and the Au particles coated with 40 monolayers of Pb. (b) Period versus Pbcoverage for the Au–Pb core–shell nanoparticles. The line shows the results fromcontinuum mechanics calculations for these particles.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
that the particles with >80% Au have spectra that closely resemble pure Au(see Fig. 6) but have a dynamic response that is controlled by Pt. This occursbecause (1) the electron–phonon coupling constant for Pt is much larger thanthat for Au and (2) Pt has a much larger density of states at the Fermi levelthan Au [19].Coherently excited acoustic vibrational modes can also be observed forbimetallic particles. Pt and Au have very similar elastic modulii; therefore,the vibrational periods observed for Pt–Au core–shell particles are very similarto those for pure Au particles of the same size. A more interesting situationarises where the two metals have different elastic properties. Figure 8ashows transient bleach data for pure Au particles and for the Au particlescoated with 40 monolayers of Pb, where modulations due to the coherentlyexcited breathing mode of the particle can be seen [17]. Clearly, the addition ofthe Pb has a strong affect on the period.Figure 8b shows the measured frequency (in cm -1 units) versus thenumber of Pb atomic layers for all the samples investigated. It is important tonote that the decrease in the frequency with increasing Pb content cannot bereproduced by using Eq. (3) and average values of c l and c t , that is, theinterface between the core and shell must be explicitly taken into account [17].The solid line in Fig. 8b shows the results of continuum mechanics calculationsfor the breathing mode of a core–shell particle. In these calculations,the displacement and normal stress were set to be continuous at the interface,and the bulk elastic properties of Au and Pb were used, details of the theoryare given in Ref. 48. The experimental results and calculations are in excellentagreement. This shows that continuum mechanics gives an excellent descriptionof the elastic properties of core–shell nanoparticles. Furthermore, even ata few atomic layers (
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Copyright 2004 by Marcel Dekker, In
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This book covers several topics of
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esult, some exciting topics were no
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3. Fine Structure and Polarization
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9. III-V Quantum Dots and Quantum D
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ContributorsUri BaninThe Hebrew Uni
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1‘‘Soft’’ Chemical Synthesi
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structure of energy states leads to
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growth can proceed by Ostwald ripen
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Figure 3 Transmission electron micr
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Figure 4 Temporal evolution of the
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No. 26, are f85% (Fig. 6) [21]. Alt
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tion spectra and broad PL spectra.
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ing surface-to-volume ratio with di
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Figure 8 Photoluminescence spectra
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lattice mismatch. Such a large latt
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match between InAs and ZnS of f11%.
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successfully repeated for up to thr
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Under a different growth regime, on
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Figure 14 Atomic model of the CdSe
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‘‘Teardrop-shaped’’ particl
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Figure 17 High-resolution TEMs of C
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allows isolation of tetrapods in f8
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ligand concentrations yield a reduc
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een determined and quantitatively c
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tion volumes were also shown to be
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synthesis temperatures of z400jC ar
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Figure 23 (a) Photoluminescence spe
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levels (fV1 Mn per NQD). Despite in
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Figure 25 X-ray diffraction pattern
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Figure 27 Transmission electron mic
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An additional factor that strongly
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Figure 30 (a,b) Schematics illustra
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Slow, controlled precipitation of h
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Figure 34 Schematic illustrating th
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achieving biological compatibility
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47. Yu H.; Gibbons P.C.; Kelton K.F
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2Electronic Structure inSemiconduct
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Figure 2 (a) Simple model of a nano
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electron and hole to be treated as
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independently, Eq. (13) is commonly
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a better description of the bulk ba
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investigated. For optical experimen
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Figure 4 (a) Absorption (solid line
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Figure 6 Normalized PLE scans for s
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Figure 8 A simplistic model for des
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Figure 10 Theoretically predicted p
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Figure 12 Schematics depicting the
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Figure 14 Calculated band-edge exci
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Figure 15 Absorption (solid line) a
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Figure 18 (a) Calculated band-edge
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IV.BEYOND CdSeA. Indium Arsenide Na
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the six-band Luttinger Hamiltonian.
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11. Norris, D.J.; Efros, Al.L.; Ros
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69. Gaponenko, S.V.; Woggon, U.; Sa
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formation of a long-lived dark exci
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where the constant A is determined
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In crystals for which the function
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The respective wave functions areC
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passive, as was shown in Ref. 12. T
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square of the matrix element of the
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where e F = e F ieV and e F F = e x
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see that for all nanocrystal shapes
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optical recombination of the excito
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B. Recombination of the Dark Excito
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where x = cos h and f = l B g e H/3
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The theory of the polarization memo
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Figure 7 The size dependence of the
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state would have an infinite lifeti
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crystal axis [see Eq. (40)]. As a r
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time of the exciton momentum relaxa
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One must also account for the influ
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observed in one of the first studie
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REFERENCES1. Bawendi, M.G.; Wilson,
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4Intraband Spectroscopyand Dynamics
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The solid line in Fig. 1 shows the
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Figure 2 FTIR spectra of n-type CdS
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of the center frequency. The experi
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limit given by radiative relaxation
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from a long lifetime due to the pho
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are two natural approaches to study
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32. Inoshita, T.; Sakaki, H. Physic
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continuous spectral tunability over
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function and envelope function mome
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ottleneck’’ [14,28]. Further re
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in NQDs is dominated by nonphonon e
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Figure 4 Dynamics of the IR postpum
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Figure 5 (a) Time-resolved PL spect
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Figure 6 (a) The time delay of the
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and due to Auger-type e-h interacti
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Figure 9 Dynamics of the 1S bleachi
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significantly greater than the fast
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Figure 11 (a) Pump-intensity-depend
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NQD size. For small NQD sizes (R =
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Figure 14 Nonlinear absorption/gain
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sorption change associated with a s
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where n h em is the hole ‘‘emit
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ultrafast (subpicosecond to picosec
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Figure 18 Schematic of transitions
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Figure 19 Dynamics of pump-induced
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where n i (i=1, 2 . . . , N ) is th
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Figure 21 (a) Two-e-h-pair (biexcit
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the volume fraction (filling factor
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intensity dependence of this peak (
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can contribute to the saturation of
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coupling between ‘‘volume’’
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numerous discussions on the photoph
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53. Kang, K.; Kepner, A.; Gaponenko
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the ‘‘on-off ’’ emission in
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parallel form of data acquisition i
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Figure 3 (a) Spectral time trace of
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transition energies. In fact, these
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distribution (dark line) does not d
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exposure to only room light. In our
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statistics for the off times are in
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230Shimizu and BawendiCopyright 200
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Figure 10 (a) Time trace of a CdSe(
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and excited QD core states to fluct
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arrows indicate the on-time truncat
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W. K. Woo and V. C. Sundar for assi
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size allows the electron affinity a
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II.THEORY OF ELECTRON TRANSFER BETW
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For the specific case of charge tra
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dominates, the mobility is often fi
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where the constant A and the temper
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components of modulation which are
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nanocrystals [41], understanding ph
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and ionization potential through tw
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quantum dots. Furthermore, because
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For many applications, a host mater
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form blends with morphologies that
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Figure 11 Photoluminescence efficie
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Figure 12 (a) Room-temperature PIA
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discussed briefly in Section IV. Ch
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dithiolates to thiol-terminated DNA
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Films of passivated CdSe nanocrysta
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Figure 16 Photocurrent action spect
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decay with stretched exponential ki
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siderably larger than might be esti
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dispersing CdSe nanocrystal chromop
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memory and charge storage effects [
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all) of the optically excited elect
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composites of nanocrystals and conj
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55. Asbury, J.B.; Hao, E.C.; Wang,
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108. Morgan, N.Y.; Leatherdale, C.A
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The approaches to fabrication of se
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Figure 1 Experimental realization o
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Due to this voltage division, the m
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Figure 3 Simulated tunneling spectr
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electron charging. In both positive
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Figure 5 shows the typical features
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Figure 7 Map of levels for InAs nan
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Figure 8 Scanning electron microsco
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D CB = 0.31 eV is thus obtained. On
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Figure 11 Correlation of optical an
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atomistic approach based on pseudop
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charging indicated that the tunneli
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capacitance values were also kept t
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could not be detected in the QD/DT/
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Figure 18 Tunneling conductanceF sp
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data in the inset of Fig. 19 repres
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corresponding to the s-like wave fu
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7. Grabert, H.; Devoret, M.H., Eds.
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66. Su, B.; Goldman, V.J.; Cunningh
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dimensional confinement are created
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Figure 1 Transmission electron micr
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The room-temperature absorption and
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narrower in samples with larger mea
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GaInP 2 QDs from a plot of the squa
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crystal, indicating lattice-matched
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Figure 5 Evolution of Stranski-Kras
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C. Efficient Anti-Stokes Photolumin
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Because HF treatment has been shown
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intensity of the PL when it is on a
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eV stems from recombining carriers
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Figure 16 Model to explain two-colo
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although this term is not rigorousl
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10 ps (about an order of magnitude
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electron relaxation is inhibited an
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QDs, the nature of the QD capping s
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QD solution. For an interdot distan
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emission spectra of the two individ
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Figure 23 Change of the PL intensit
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(viz. the absorbed light intensity)
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Figure 25Impact ionization in QDs.m
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prevent electron-hole recombination
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36. Miller, R.D.J.; McLendon, G.; N
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91. Vurgaftman, I.; Singh, J. Appl.
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139. Mićić, O.I.; Ahrenkiel, S.P.
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10Synthesis and Fabrication of Meta
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Figure 2 (A-C) Progression of HR-TE
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Figure 3 Schematic for gold nanocry
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Nanocrystal growth can occur by two
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on the other hand, provide an ensem
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Figure 6 (a) SAXS patterns for disp
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Figure 8 The gold nanocrystal film
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of the stabilizing ligand, and the
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successfully modeled the 2D island
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2. Steric Stabilization and a Soft
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are fully extended. Moving away fro
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Figure 11 High-resolution SEM image
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Figure 13 (A) Transmission electron
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function of the density of localize
Page 429 and 430: Figure 15 High-resolution SEM image
Page 431 and 432: thiol-capped nanocrystals [2]. The
Page 433 and 434: 41. Ackerson, B.J. Nature 1993, 365
Page 435 and 436: with the effect of the particle com
Page 437 and 438: Figure 1a shows the surface plasmon
Page 439 and 440: Figure 2 (a) Ultraviolet-visible ab
Page 441 and 442: agents [34]. The short-wavelength b
Page 443 and 444: Figure 4 (a) Plot of the plasmon ab
Page 445 and 446: the framework of traditional Mie’
Page 447 and 448: show that effects due to the surrou
Page 449 and 450: is located at the position of the g
Page 451 and 452: Copyright 2004 by Marcel Dekker, In
Page 453 and 454: Figure 8 Ultraviolet-visible absorp
Page 455 and 456: laser pulses while being mixed in t
Page 457 and 458: Figure 10 shows HR-TEM images of go
Page 459 and 460: Figure 11 Transmission electron mic
Page 461 and 462: final irradiation product. At the s
Page 463 and 464: following the laser excitation appe
Page 465 and 466: 36. Papavassiliou, G.C. Prog. Solid
Page 467 and 468: particles to expand. Because the he
Page 469 and 470: was frequency doubled in a 1-mm B-
Page 471 and 472: Figure 2 Frequency of the acoustic
Page 473 and 474: Figure 3 Change in radius (DR/R) ve
Page 475 and 476: In this model, the electrons couple
Page 477 and 478: Figure 5 Transient bleach data for
Page 479: Figure 7 (a) Transient bleach data
Page 483 and 484: 3. Del Fatti, N.; Valle´e, F.; Fly
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